The field of this invention relates to visual indicators of pressure, particularly on valve stem seals, which act as a warning to personnel to relieve such pressure prior to attempting any disassembly.
Valves of all types have been in use in the oil and gas industry for a variety of purposes. Valves have typically had stems that extend through their bodies with a manual or powered operator attached to the stem. Depending on the valve design these stems could be of the rising or non-rising type. The stem would feature a sealing system to prevent pressure inside the valve body from escaping. Stem seals could involve packing or seal rings or combinations of such devices. In some valves, there were two stem seals with access to an annular space between them through an opening, which was plugged or had a grease fitting. Some illustrative examples are U.S. Pat. Nos. 5,129,624: 3,544,064(illustrating the use of a grease fitting): and 4,575,101. In some applications, the access to the annular space between an upper and lower stem seal featured the ability to add a sealing material under pressure or to mount a detector to sense leakage into the annular space between the stem seals. Some illustrative examples are U.S. Pat. Nos. 4,972,867; and 4,364,542. In yet another example, in U.S. Pat. No. 4,230,299 the annular space between the two stem seals is in communication with a plug, which blows out upon leakage of a stem seal. This design is clearly inapplicable to toxic service because it may be fatal to personnel if the plug 144 blows at an inopportune time. Additionally, the fact that the plug 144 is not in place may be indicative of the fact that the plug was never installed or that, in the past, there was a leak past a stem seal but there may be no leakage problem at the present time.
In other designs, the annular area between the stem seals would be pressurized to a higher pressure level than seen in the valve body. This auxiliary pressure system would have a pressure source and a pressure accumulator chamber as well as some indication of the pressure in the auxiliary system being applied to the annular space. Pressure and fluid detectors were sometimes combined with such systems. Some examples are U.S. Pat. Nos. 5,244,183(note the pressure indicating rod 81 on the accumulator 34); and 5,211,532(note hinged flaps 73 which turn responsively to piston movement signaling fluid addition to the annular space).
The auxiliary systems just described had several negative attributes, which limited their application. These systems were expensive, took up space unavailable in some applications, added weight, increased fit-up time, and required additional maintenance above and beyond routine valve maintenance. The issue of routine valve maintenance raises important personnel safety questions. It is very unsafe for personnel to disassemble valve bonnets for the purpose of stem seal inspection or replacement when there is trapped pressure between the stem seals. Undeniably, some personnel are better trained in safety procedures. To these people it is a matter of routine to always vent the annular space between the stem seals before loosening the top bonnet. This can be simply accomplished by removing a plug in an opening in fluid communication with the annulus between the stem seals or, if there is one, by opening a valve in communication with the annulus. The problem is that some personnel are not as diligent and could release the bonnet with pressure on the upper stem seal. The released fluid or the bonnet being propelled by fluid pressure could cause a severe injury. One other attempt to deal with this problem in the past has been to put enough thread on the bonnet or its fasteners to allow pressurized fluid venting while the bonnet is still engaged to the valve body by a few threads. This procedure also raised several safety issues. If the fasteners or the bonnet were turned too quickly or if the threads failed to hold a severe accident could occur. Other valve designs of general interest are U.S. Pat. Nos. 4,940,208; 4,497,340; 4,510,966; and 4,813,648.
What is needed is a new paradigm in signaling operations and maintenance workers of the potential dangers of trapped fluid under a stem seal. The object of this invention is to provide just such a solution, which, upon more universal use in the industry, will reduce personal injuries when valves are inspected and maintained. In order to accomplish this ambitious goal, the proposed solution must be so simple in operation and readily integrated into existing valve body molds that it will gain universal acceptance. The objective of the present invention is to fulfill this need in the industry with a simple, economical design that, at a glance, provides the needed warning that pressure exists in the annular space between the stem seals. Those skilled in the art will appreciate how the objective of the invention is met by a review of the description of the preferred embodiment, which appears below.
A visual signal of pressure between valve stem seals is given by a rising ring, which moves upwardly with the upper stem seal when there is pressure between the stem seals. The rising ring is held to the stem or valve body around the stem by a retaining ring. The rising ring, in its up position, precludes removal of the retaining ring.